Poor Performance gdc11 for base 64 with O3

[Siarhei Siamashka]

On Sunday, 19 September 2021 at 19:31:27 UTC, max haughton wrote:
> On Sunday, 19 September 2021 at 19:04:28 UTC, Mahdi wrote:
>> In optimization level 3, gdc11 doesn't seem to work as well as 
>>  gdc10 for base 64 benchmark.
>> On this site:
>> https://github.com/kostya/benchmarks#base64
>>
>> [...]
>
> It's because of libphobos not being compiled with inlining due 
> to the changes to template linkage emission.

Could you please tell me more about these changes? Are they 
somewhere in the GDC frontend, GCC backend or in the libphobos 
code itself? Were they intentional or a side effect of something 
else?

Before finding this forum thread, I happened to submit a similar 
issue in the gcc bugzilla some days ago: 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102765

What is the current status of LTO nowadays? Is it sufficiently 
reliable and problem-free in GDC11 to be universally recommended 
for any optimized release builds?